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Risk Management Activities - Maturity of Non-Hedges (Details) - 12 months ended Dec. 31, 2020 - Non-Hedges - Commodity risk management | CAD ($) $ / $ | cADPerMegawattHour
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Foreign exchange forward contracts – foreign-denominated receipts/expenditures | Within one year |  |
Disclosure of maturity analysis for non-derivative financial liabilities [line items] |  |
Notional amount | $ 54,000,000 |
Average foreign exchange rate | $ / $ | 0.7648 |
Foreign exchange forward contracts – foreign-denominated receipts/expenditures | 2022 |  |
Disclosure of maturity analysis for non-derivative financial liabilities [line items] |  |
Notional amount | $ 0 |
Average foreign exchange rate | $ / $ | 0 |
Foreign exchange forward contracts – foreign-denominated receipts/expenditures | 2023 |  |
Disclosure of maturity analysis for non-derivative financial liabilities [line items] |  |
Notional amount | $ 0 |
Average foreign exchange rate | $ / $ | 0 |
Foreign exchange forward contracts – foreign-denominated receipts/expenditures | 2024 |  |
Disclosure of maturity analysis for non-derivative financial liabilities [line items] |  |
Notional amount | $ 0 |
Average foreign exchange rate | $ / $ | 0 |
Foreign exchange forward contracts – foreign-denominated receipts/expenditures | 2025 |  |
Disclosure of maturity analysis for non-derivative financial liabilities [line items] |  |
Notional amount | $ 0 |
Average foreign exchange rate | $ / $ | 0 |
Foreign exchange forward contracts – foreign-denominated receipts/expenditures | More than five years |  |
Disclosure of maturity analysis for non-derivative financial liabilities [line items] |  |
Notional amount | $ 0 |
Average foreign exchange rate | $ / $ | 0 |
Electricity | Within one year |  |
Disclosure of maturity analysis for non-derivative financial liabilities [line items] |  |
Notional amount | $ 3,424,000 |
Average power prices | cADPerMegawattHour |  | cADPerMegawattHour 69.51
Electricity | 2022 |  |
Disclosure of maturity analysis for non-derivative financial liabilities [line items] |  |
Notional amount | 3,329,000 |
Average power prices | cADPerMegawattHour |  | 71.91
Electricity | 2023 |  |
Disclosure of maturity analysis for non-derivative financial liabilities [line items] |  |
Notional amount | 3,329,000 |
Average power prices | cADPerMegawattHour |  | 73.72
Electricity | 2024 |  |
Disclosure of maturity analysis for non-derivative financial liabilities [line items] |  |
Notional amount | 3,338,000 |
Average power prices | cADPerMegawattHour |  | 75.56
Electricity | 2025 |  |
Disclosure of maturity analysis for non-derivative financial liabilities [line items] |  |
Notional amount | 2,628,000 |
Average power prices | cADPerMegawattHour |  | 77.44
Electricity | More than five years |  |
Disclosure of maturity analysis for non-derivative financial liabilities [line items] |  |
Notional amount | $ 0 |
Average power prices | cADPerMegawattHour |  | cADPerMegawattHour 0

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